A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network the computing devices communicate data by dividing the data into small blocks called packets. Certain devices within the network, such as routers, maintain routing information that describes routes through the network. In this way, the packets may be individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Virtual private local area network service (VPLS) instances are often used to extend two or more remote customer networks, i.e., VPLS sites, through a public network, such as the Internet, as if the public network does not exist. VPLS instances often transport layer two (L2) communications, such as Ethernet packets, between customer networks via the public network. In a typical configuration, routers coupled to the customer networks define label switched paths (LSPs) within the public network to carry encapsulated L2 communications as if these customer networks were directly attached to the same LAN.
In some cases, a VPLS multicast instance may be configured to carry L2 multicast traffic, such as Internet Protocol Television (IPTV), desktop conferences, corporate broadcasts, music and video web casts, and other forms of multimedia content. VPLS multicast instances typically rely on ingress replication to transmit the multicast traffic from a multicast source to subscriber devices within the customer networks. Ingress replication causes an ingress router of a VPLS to replicate a multicast data packet of a particular multicast group and send it to each egress router of the VPLS on the path to a subscriber device of that multicast group. However, ingress replication may be a reasonable model only when the bandwidth of the multicast traffic is low and/or the number of replications performed by the ingress router for a particular multicast data packet is small.
In order to send multicast packets only to the egress routers of the VPLS that have subscriber devices for that traffic, the ingress router of the VPLS may use internet group management protocol (IGMP) snooping or protocol independent multicast (PIM) snooping between the routers and the customer networks. However, each router in the network then has to maintain state for all of the multicast source and group (S,G) entries in each of the VPLS multicast instances to which the router belongs. In addition, the PIM snooping is also performed on pseudo-wire (PW) interfaces between the routers within the network. This introduces a non-negligible overhead on the routers.